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Maintaining a good level of physical fitness is something that we should all aspire to do. But it can be difficult to determine what fitness entails. Here we answer the question: what does being physically fit mean?

According to the United States Department of Health and Human Services, physical fitness is defined as "a set of attributes that people have or achieve that relates to the ability to perform physical activity."

This description goes beyond being able to run fast or lift heavy weights. Despite being important, these attributes only address single areas of fitness. This article provides details of the five main components of physical fitness.

Fast facts on fitness:

Maintaining physical fitness can help prevent some diseases.

With exercise, body composition can change without changing weight.

Athletes' hearts show different changes dependent on their chosen sport.

Muscle strength increases by fiber hypertrophy and neural changes.

Stretching to increase flexibility can ease a number of medical complaints.

Overview

Being physically fit depends on how well a person fulfills each of the components of being healthful.

When it comes to fitness, these components include

cardiorespiratory fitness

muscular strength

muscular endurance

body composition

flexibility.

So, you can tell if someone is physically fit by determining how well they perform in each component.

Here we will look at them all individually.

Cardiorespiratory performance

Cardiorespiratory endurance indicates how well our body can supply fuel during physical activity via the body's circulatory and respiratory systems. Activities that help improve cardiorespiratory endurance are those that cause an elevated heart rate for a sustained period.

These activities include:

swimming

brisk walking

jogging

cycling

People who regularly take part in these activities are more likely to be physically fit in terms of cardiorespiratory endurance. It is important to begin these activities slowly and gradually increase the intensity.

Exercising increases cardiorespiratory endurance in a number of ways. The heart muscle is strengthened so that it is able to pump more blood per heartbeat.

At the same time, additional small arteries are grown within muscle tissue so that blood can be delivered to working muscles more effectively when needed.

How does heart health change with exercise?

The heart changes and improves its efficiency after persistent training. However, more recent research shows that different types of activity change the heart in subtly different ways.

All types of exercise increase the heart's overall size, but there are significant differences between endurance athletes, like rowers, and strength athletes, like football players. Endurance athletes' hearts show expanded left and right ventricles, whereas strength athletes show thickening of their heart wall, particularly the left ventricle.

How does lung health change with exercise?

While the heart steadily strengthens over time, the respiratory system does not adjust to the same degree. Lung function does not drastically change, but oxygen that is taken in by the lungs is used more effectively.

In general, exercise encourages the body to become more efficient at taking on, distributing, and using oxygen. This improvement, over time, increases endurance and overall health.

The American College of Sports Medicine recommends aerobic exercise 3-5 times per week for 30-60 minutes, at an intensity that keeps the heart rate at 65-85 percent of the maximum heart rate.

Health benefits of cardiorespiratory fitness

Cardiorespiratory fitness has been found to help reduce the risk of conditions including:

Strength

The U.S. Department of Health and Human Services defines muscular strength as "the ability of muscle to exert force during an activity."

There are a number of ways to measure muscular strength. Generally, lifting or pushing something of a set weight in a prescribed position and comparing the results against any given population is the best way.

In general, if a muscle is worked consistently and regularly, it will increase in strength. There are various ways of putting your muscles through rigorous activity, but anything that works a muscle until it is tired will increase muscle strength over time.

How does muscle structure change with exercise?

Muscles consist of elongated muscle cells. Each muscle cell contains contractile proteins - actin and myosin - that give the muscle its strength. These fibers contract together, producing the so-called power stroke. The total force depends on the number of these units contracting in unison.

To build muscle, the following criteria must be met:

muscles are regularly exercised

the individual has taken in enough protein

The exact mechanism of muscle building is not fully understood, but the general principles are well known. Training causes the muscle cells to expand and there is an increase in actin and myosin production.

Also, in untrained muscles, fibers tend to fire in an asynchronous manner - in other words, they do not fire in unison. As they become trained, they learn to fire together as one, increasing maximum power output.

Normally, the body prevents the muscles from over-exerting themselves and becoming injured. As the muscle is trained, the body starts to disinhibit the muscles' activation - more power is allowed to be exerted.

Endurance

Fitness can include muscular endurance, which is the ability of a muscle to continue exerting force without tiring. As mentioned above, strength training builds bigger muscles. Endurance training, on the other hand, does not necessarily generate muscles of a larger size.

This is because the body focuses more on the cardiovascular system, ensuring that the muscles receive the oxygenated blood they need to keep functioning. Another important change in muscles that are specifically trained for endurance concerns the different types of muscle tissue - fast twitch and slow twitch fibers:

Fast twitch fibers - contract quickly but get tired quickly. They use a lot of energy and are useful for sprints. They are whitish in color as they do not require blood to function.

Slow twitch fibers - best for endurance work, they can carry out tasks without getting tired. They are found in core muscles. These fibers appear red as they rely on a good supply of oxygenated blood and contain stores of myoglobin.

Different exercises will promote fast twitch fibers, slow twitch fibers, or both. A sprinter will have comparatively more fast twitch fibers, whereas a long distance runner will have more slow twitch fibers.

How is body composition calculated?

Caclulating body composition accurately can be a painstaking task. There are a number of accurate methods, this is just one:

First, weight is measured on standard scales. Next, volume is measured by submerging the individual in water and measuring the displacement.

The proportions of water, protein, and mineral in the body can be ascertained by various chemical and radiometric tests. The densities of water, fat, protein, and mineral are either measured or estimated.

Flexibility

Flexibility is the range of movement across a joint. Flexibility is important because it improves the ability to link movements together smoothly and can help prevent injuries. Flexibility is specific to each joint and depends on a number of variables, including the tightness of ligaments and tendons.

Flexibility is increased by various activities, all designed to stretch joints, ligaments, and tendons. There are three types of exercise that are generally utilized to increase flexibility:

Dynamic stretching - the ability to complete a full range of motion of a particular joint. This type of flexibility is used in standard "warming up" exercises as it helps ready the body for physical activity.

Static-active stretching - holding the body or part of the body in a stretched position and maintaining that position for a period of time. One example of static-active stretching is the splits.

Ballistic stretching - only to be used when the body is already warmed up and limber from exercise, it involves stretching in various positions and bouncing.

There are a number of ways to improve flexibility. A daily stretching regimen can be the simplest and most efficient way of achieving whole body flexibility.

Takeaway

In general, fitness means different things to different people. The important take-home message is that embarking on any regular exercise will be of benefit to your health. The more exercise that is carried out, the healthier an individual will look and feel.

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